The Structure of Copper(II)-Histidine Chelate
THE QUESTION OF THE INVOLVEMENT OF THE IMIDAZOLE GROUP
Bibudhendra Sarkar 1 and Yuk Wigfield 1
From the
1 From the Division of Biochemistry, The Research Institute of the Hospital for Sick Children, Toronto 2, Ontario, Canada
The binding of Cu(II) by histidine in 1:2 molar ratio has been investigated. The theoretical number of hydrogen ions displaced from each mole of bound ligand at several pH values was calculated considering all the possible interactions between Cu(II) and histidine involving (a) amino and carboxyl, (b) amino and imidazole, (c) imidazole and carboxyl, and (d) amino, imidazole, and carboxyl groups. When determined experimentally by discontinuous titration, the number of hydrogen ions coincided with the number consistent with the amino and carboxyl binding and strongly suggested that the imidazole moiety is not involved. Similar studies with Cu(II)-histamine, Cu(II)-alanine, and Cu(II)-imidazole confirmed the accepted views regarding their metal binding sites. No resemblance could be seen in the ultraviolet spectra between Cu(II)-histidine and Cu(II)-imidazole. Samples of Cu(II)-histidine, Cu(II)-histamine, and Cu(II)-alanine showed absorption maxima between 235 and 242 mµ which strongly suggested that the 
max of Cu(II)-histidine in the ultraviolet region is most likely due to Cu(II) binding to amino and not to imidazole. Infrared spectrum of Cu(II)-histidine in D2O solution exhibited a strong shift in the antisymmetric carboxyl stretching frequency which is consistent with the coordination of the carboxyl group.
Submitted on June 19, 1967
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
